TVS structures for high surge and low capacitance

ABSTRACT

A transient voltage suppressing (TVS) device formed in an epitaxial layer of a first conductivity type supported on a semiconductor substrate. The TVS device further comprises a plurality of contact trenches opened and extended to a lower part of the epitaxial layer filled with a doped polysilicon layer of a second conductivity type wherein the trenches are further surrounded by a heavy dopant region of the second conductivity type. The TVS device further includes a metal contact layer disposed on a top surface of the epitaxial layer electrically connected to a Vcc electrode wherein the metal contact layer further directly contacting the doped polysilicon layer and the heavy dopant region of the second conductivity type.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to a device structure and manufacturemethod of a transient voltage suppressor (TVS). More particularly, thisinvention relates to an improved device structure and manufacture methodof TVS devices to handle dissipation of large amount of energy during ahigh transient surge and in the meantime maintaining a low capacitancefor a transient voltage suppressor (TVS).

2. Description of the Relevant Art

The device configurations and method of manufacturing the transientvoltage suppression (TVS) device are still confronted with the technicalchallenges that the TVS device fails due to overheating in handle alarge amount of energy dissipation in the process of suppressing thetransient voltage. Specifically, the transient voltage suppressors (TVS)are commonly applied for protecting integrated circuits from damages dueto the inadvertent occurrence of an over voltage imposed onto theintegrated circuit. An integrated circuit is designed to operate over anormal range of voltages. However, in situations such as electrostaticdischarge (ESD), electrical fast transients and lightning, an unexpectedand an uncontrollable high voltage may accidentally strike onto thecircuit. The TVS devices are required to serve the protection functionsto circumvent the damages that are likely to occur to the integratedcircuits when such over voltage conditions occur. As increasing numberof devices are implemented with the integrated circuits that arevulnerable to over voltage damages, demands for TVS protection are alsoincreased. Exemplary applications of TVS can be found in the USB powerand data line protection, Digital video interface, high speed Ethernet,Notebook computers, monitors and flat panel displays.

The challenges for the TVS device to absorb large amount of energy inshort period of time is increased due to the requirements of the TVSperformance with common IEC 61000 Standards of 8×20 μSecs, 10×1000 μSecspulse surge current. With large amount of energy dissipation, the mostcommon TVS failures often occur when the metal melts down due tooverheating. It is well known that the silicon as part of the TVS devicecan sustain significant higher power dissipation than the metal. Whilethe metal layer often formed near the top surface of the TVS structureand commonly implemented as electrodes or electrical contacts, the metallayer tends to melt down due to overheating. The over voltage protectionfunctions of the TVS device are therefore compromised due to these meltdown failures.

FIG. 1 is a cross sectional view of a conventional TVS device. Thedevice structure has an intrinsic limitation due to a shallow blockingjunction caused by a topside N diffusion manufacturing process. As aresult, the voltage blocking region is closer to the surface that isnear to the metal layer commonly formed on the top surface as electricalcontacts. As the semiconductor device experiences a high transientvoltage surge, the blocking junction absorbs a large amount of energythus causing the temperature to rise rapidly. The elevated temperaturetakes place locally near the metal may lead to overheating followed bymelting the metal disposed near the blocking junction area thus causesthe TVS to fail.

Therefore, a need still exists to provide new manufacture methods forthe TVS devices with improved processes to produce new device structuressuch that the above discussed problems and limitations can be resolved.

SUMMARY OF THE PRESENT INVENTION

It is therefore an aspect of the present invention to provide animproved TVS structural configurations manufactured with new andimproved processes to provide better surge performance withoutcompromising the voltage clamping capabilities of the TVS devices.

In the present invention, the steering diodes are integrated with a mainZener diode where the high-side diode, the low-side diode and the mainZener diode are all manufactured as vertical diodes in a semiconductorsubstrate with simplified layer structures. The high-side diode overlapswith the main Zener diode such that the TVS device occupiessignificantly less area. Meanwhile, the device configuration is improvedby forming multiple PN junctions with a laterally extended N-buriedlayer in a P epitaxial layer below a N− top dopant layer and a P+contact region to constitute a bottom Zener diode and simultaneouslyfunction as a silicon controlled rectifier (SCR) acting as a high sidesteering diode. The device further significantly reduces the capacitancebecause of the series connection of the equivalent capacitances formedby the PN junctions of the SCR. In a preferred embodiment, the N− topdopant layer has low doping concentration, which further decreases thecapacitance. Preferably, the N− top dopant layer portion of the SCR isfloating and completely depleted at a zero bias so that the SCRfunctions like a normal diode with low capacitance. Therefore, the abovediscussed technical difficulties and challenges are resolved.

Briefly in a preferred embodiment this invention discloses atransient-voltage suppressing (TVS) device disposed on a semiconductorsubstrate of a first conductivity type. The TVS device includes aplurality of contact trenches opened and extended to a lower part of theepitaxial layer filled with a doped polysilicon layer of a secondconductivity type where the trenches are further surrounded by a heavydopant region of the second conductivity type; and a metal contact layerdisposed on a top surface of the epitaxial layer electrically connectedto a Vcc electrode where the metal contact layer further directlycontacts the doped polysilicon layer and the heavy dopant region of thesecond conductivity type.

In another preferred embodiment, the epitaxial layer is a P-typeepitaxial layer and the contact trenches are filled with an N-dopedpolysilicon layer surrounded by an N-type heavy dopant region. Inanother preferred embodiment, the epitaxial layer is an N-type epitaxiallayer and the contact trenches are filled with a P-doped polysiliconlayer surrounded by a P-type heavy dopant region. In another preferredembodiment, the contact trenches are filled with an N-doped polysiliconlayer surrounded by an N-type heavy dopant region; and the contact metallayer is electrically connected to a cathode electrode. In anotherpreferred embodiment, the TVS device further includes a top dopant layerof the second conductivity type disposed near the top of said epitaxiallayer. The TVS device further includes a buried dopant region of thesecond conductivity type disposed and encompassed in the epitaxial layerwhere the buried dopant region interfaces with underlying portions ofsaid epitaxial layer thus constituting a Zener diode for said TVSdevice; and a first contact region of the first conductivity typedisposed on the top of the top dopant layer over the buried dopantregion for constituting a semiconductor controlled rectifier (SCR)functioning as a first steering diode, where the SCR comprisesvertically of the first contact region, the top dopant layer, theepitaxial layer, and the buried dopant region where the first contactregion is disposed at a distance away and insulated from the contacttrenches, and the buried dopant region of the second conductivity typefurther extends laterally and merges with the heavy dopant regions ofthe second conductivity type below the contact trenches.

In another preferred embodiment, the TVS device includes a plurality ofisolation trenches isolating a section of the epitaxial layer and thetop dopant layer for isolating the SCR from the contact trenches. Inanother preferred embodiment, the TVS device further includes a secondcontact region of the second conductivity type disposed at the top ofthe top dopant layer and laterally extending in opposite side of thecontact trenches from the SCR and first steering diode, where the secondcontact region interfaces with the top dopant layer functions as asecond steering diode and together with the first steering diode forminga pair of steering diodes of the TVS device. In another preferredembodiment, the first and second steering diodes form a pair of steeringdiodes comprising a high side steering diode and a low side steeringdiode on two opposite sides of the contact trenches surrounded by thedopant regions of the second conductivity type. In another preferredembodiment, the second steering diode further includes a part of the topdopant layer for reducing the capacitance of the second steering diode.In another preferred embodiment, the first and second steering diodesare connected to an input/output (I/O) pad through the first and secondcontact regions, respectively.

In another preferred embodiment, the TVS device further comprisesisolation trenches surrounding the first and second steering diodes forinsulating the first and second steering diodes from the contacttrenches. In another preferred embodiment, the first steering diode, thesecond steering diode and the contact trenches are separated by at leastone isolation trench. In another preferred embodiment, the TVS devicefurther comprises a voltage breakdown (VBD) trigger zone formed with ahigh dopant concentration of first conductivity type in a Zener diodeoverlapping zone disposed in the epitaxial layer below the buried dopantregion to control a voltage breakdown.

In another preferred embodiment, the TVS device further comprises aninsulation layer covering a top surface of the semiconductor substratehaving openings for forming a metal contact layer contacting with thedoped conductive layer disposed in the contact trenches. In anotherpreferred embodiment, the first conductivity type is P-type and thesemiconductor substrate functions as a ground voltage (GND) terminal.

This invention further discloses a method for manufacturing a transientvoltage suppressing (TVS) device. The method includes steps of a)growing an epitaxial layer having a first conductivity type on asemiconductor substrate of the first conductivity type and opening aplurality of contact trenches in the epitaxial layer followed byimplanting a dopant region of a second conductivity type below thetrenches in the epitaxial layer; and b) filling the contact trencheswith a doped conductive layer of the second conductivity type followedby applying a mask to form dopant regions of the second conductivitytype near the top surface of the epitaxial layer followed by applying anelevated temperature to diffuse the dopant regions below each of thecontact trenches to diffuse and surround the contact trenches in theepitaxial layer. In another preferred embodiment, the method furtherincludes a step of c) forming a top insulation layer on top of theepitaxial layer and opening plurality of contact openings in the topinsulation layer followed by forming a contact metal layer forcontacting with the doped conductive layer filled in the contacttrenches and the dopant regions of the second conductivity typesurrounding the contact trenches.

These and other objects and advantages of the present invention will nodoubt become obvious to those of ordinary skill in the art after havingread the following detailed description of the preferred embodiment,which is illustrated in the various drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a conventional TVS device with the blocking junction formedby a topside N diffusion and disposed near the surface of a conventionalTVS circuit implemented with diode array commonly applied forelectrostatic discharge (ESD) protection.

FIG. 2 is a cross sectional view of an improved TVS device structure asan embodiment of this invention.

FIGS. 3A to 3F are a series of cross sectional views for illustratingthe manufacturing processes for making the TVS device of this invention.

FIG. 4A is a cross sectional view of an improved TVS device of thisinvention that includes integrated Zener diode with the depleted SCRhigh side structure and the low side steering diode.

FIG. 4A-1 shows the equivalent circuit of this device structure.

FIG. 4B is a close up view taken from the top of FIG. 4A showing theequivalent capacitances of the circuit. FIG. 4C is the same crosssectional view as shown in FIG. 4A-1, but with the conductivity typesreversed.

FIGS. 5A to 5K are cross sectional views for illustrating the forming ofthe TVS device of FIG. 4A

DETAILED DESCRIPTION OF THE METHOD

This Patent Application is related to application Ser. No. 13/720,140filed on Dec. 19, 2012 by a common inventor of this Application andissued into U.S. Pat. No. 8,835,977. Application Ser. No. 13/720,140 isa Divisional Application of another application Ser. No. 12/384,185filed on Mar. 31, 2009 and now issued into U.S. Pat. No. 8,338,854. Thedisclosures of application Ser. Nos. 12/384,185 and 13/720,140 arehereby incorporated by reference in this Patent Application.

FIG. 2 is a cross sectional view of a TVS structure 100 supported on aP-type epitaxial layer 105 supported on a semiconductor substrate (notshown) according to an embodiment of the present invention. The TVSstructure includes a plurality of trenches filled with N+ polysiliconlayer 120 and the trenches are surrounded by N+ dopant regions 110.Preferably the trenches are opened from the top surface of the epitaxiallayer 105 and extend into a lower portion of the epitaxial layer 105. Ametal contact layer 150 is in contact with the N+ polysilicon layer 120and the N+ dopant regions 110. The metal contact layer 150 is furtherinsulated from the I/O pad (not shown) of the TVS device by aninterlayer dielectric (ILD) layer 140, e.g., a BPSG layer. In onepreferred embodiment, the N+ polysilicon layer 120 extend above the topsurface of the epitaxial layer such that the top portion of the N+polysilicon layer 120 extending above the top surface of the epitaxiallayer contacts the metal contact layer 150 on its entire surface. N+dopant regions 110 extends over the entire epitaxial layer betweenadjacent trenches. The N+ dopant regions 110 further include a surfaceportion 130 adjacent the top surface of the epitaxial layer extendinglaterally to a width wider than a width of the rest of the N+ dopantregions 110 surrounding the side walls of the trenches below the surfaceportion.

In the TVS structure of this invention, the peak E field and the voltageblocking region are moved significantly down into the bulk region of theepitaxial layer 105 in the semiconductor substrate. The deep junctionregion is formed without a need for applying an extreme thermal cycle byusing deep trenches. The trenches are filled with N+ doped polysiliconlayer 120 to allow excellent current conduction. Because of the goodconductivity in the upper parts of the TVS structure, there is no Efield on the device topside; therefore, the polysilicon region is fieldfree. The major power dissipation at high surge event happens atjunction area, which is pushed deep down into silicon, further away frommetal. Therefore, this configuration resolves the problem of metaloverheating and device failures encountered by the conventional TVSstructure when large energy dissipation occurs in a high voltage surge.

FIGS. 3A to 3F are a series of cross sectional views for showing themanufacturing processes to make a TVS structure 100 of FIG. 2 accordingto an embodiment of the present invention. In FIG. 3A, an oxide layer109 is formed on top of silicon epitaxial layer 105 as a hardmask for asubsequent trench etch process. A plurality of trenches 107 are thenformed from the top surface of the epitaxial layer 105, preferablyextending into a lower portion of the epitaxial layer 105. In FIG. 3B, asacrificial oxide layer is formed (not shown) followed by a phosphorusdopant implantation through the trenches 107 to form dopant regions 110below the bottom surface of the trenches 107. In an exemplary processthe phosphorus implantation is carried out with dopant concentration of5e14 and implant energy of 200 Kev. In FIG. 3C, the sacrificial oxidelayer (not shown) is removed followed by carrying out an insitupolysilicon deposition to form the polysilicon layer 120 to fill in thetrenches and covering over the top surface of the oxide layer 109. InFIG. 3D, an etch-back process is performed to etch back the polysiliconlayer 120 to the top surface of the oxide layer 109 followed by an oxideetch to strip the oxide layer 109 from the top surface of the epitaxiallayer 105. In exemplary processes the polysilicon may be etched with dryetch of CMP and the oxide can be etched by either a dry or wet etchwhile the wet etch process is preferred. In FIG. 3E, a mask (not shown)is applied to implant dopant ions, e.g., phosphorus or Arsenide, to formregions 130 near the top surface of the epitaxial layer 105 followed byremoving the mask (not shown). In FIG. 3F, a diffusion process at atemperature of 1150 degrees Celsius is performed for 30 minutes for thedopant regions 110 and region 130 to diffuse and merge together aroundthe trenches filled with the polysilicon layer 120. Then an interlayerdielectric (ILD) layer 140 composed of an insulation material is formedon the top surface followed by applying a contact mask (not shown) toetch and open contact openings in the ILD layer 140. A metal layer 150is deposited as a metal contact to region 130 and the polysilicon layer120 filled in the trench followed by applying a metal mask (not shown)to etch and pattern the metal contact layer 150. Then the metal mask(not shown) is removed.

FIG. 4A is a cross sectional view of a TVS device 200 including atransient voltage suppressor (TVS) structure of FIG. 2 according to anembodiment of the present invention. The TVS device 200 as shown isformed with a depleted SCR high side structure using a buried N+ layer220 in a P type epitaxial region. i.e., P− epitaxial layers 210-1 and210-2, with the addition of P and N type regions, e.g., regions 240 and250 implanted from the top surface. The high side diode is formed by aP+/N−/P−/N+ (or N+/N−/P−/P+) doping profile, i.e., junctions formedbetween regions 250/215/210-2/220, to achieve a lower junctioncapacitance. Specifically, the TVS device 200 is formed on a heavilydoped P+ semiconductor substrate 205 which supports lightly doped P−epitaxial layers 210-1 and 210-2. An N− compensation dopant layer 215 islocated near the top of P− epitaxial layer 210-2. The TVS device 200includes a P+ contact region 250 formed near a top surface of the P−epitaxial layer 210-2, above the N buried region 220, to enhance theelectrical contact with the I/O pad 270. As mentioned above, the TVSdevice 200 includes an N+ buried region 220 formed in the P− epitaxiallayer 210-1 and 210-2. A semiconductor controlled rectifier (SCR) 230-1is formed between the P+ contact region 250 and the N+ buried layer220-2, and acts as the first steering diode, which in this case is thehigh side steering diode. The SCR 230-1 is formed vertically from P+contact region 250 through the N− compensation dopant layer 215 and P−epitaxial region 210-2 to the N+ buried layer 220. The N+ buried region220 is formed with an extended length beyond isolation trenches 239 tofunction with the P− epitaxial layer 210-1 below it as the main Zenerdiode 230-3 for the TVS device 200. Deep isolation trenches 239 are usedto define the boundary of the high side diode. The isolation trenches239 reduces the side wall P-N junction capacitance resulting from theuse of N+ sinker 110, since without isolation trenches 239, N+ sinker110 can be used surrounding the diode area as isolation thus resultingjunction capacitance. The isolation trenches 239 also help avoidparasitic transistor action. The isolation trenches are filled with adielectric such as oxide, which has a lower dielectric constant comparedto silicon in order to further reduce any sidewall coupling capacitance.The presence of oxide filled trenches 239 also plays an important rolein reducing the I/O-pad to substrate ground capacitance. Theinput/output (I/O) Pad capacitance is further reduced by the use ofmultiple isolation trenches in this device structure. In an alternativeembodiment, the isolation trenches 239 may comprise a polysilicon centerenclosed by oxide. The oxide filled trenches 239 may be placedsurrounding the first steering diode 230-1 in the areas where the I/Opad 270 is located to help reduce the I/O pad to substrate groundcapacitance. A Zener diode 230-3 in the overlapping zone is optionallyformed with a deep voltage breakdown (VBD) trigger implant layer 221implanted with P+ dopant ions disposed between the epitaxial layer 210-1and the N+ buried layer 220 disposed below the upper N compensationlayer 215 to control the voltage breakdown.

An N+ doped contact region 240 is formed on top of a second steeringdiode 230-2 (which in this configuration is the low side steering diode)formed between the P− epitaxial layer 210-2 and the upper N−compensation dopant layer 215. The N+ contact region 240 is formed toenhance the electrical contact, which is connected to the I/O pad in athird dimension (not shown). The second steering diode 230-2 isconnected to the Zener diode through the heavily doped semiconductorsubstrate 205. The low side steering diode 230-2 is isolated from thehigh side steering diode 230-1 in the semiconductor regions by lateraldistance and isolation trenches 239 to prevent a latch up in thesemiconductor regions. An oxide insulation layer 245 covering the topsurface of the P− epitaxial layer 210-2 has openings to allow the I/Opad 270 to make contact to contact regions 250 and 240, respectively.

The new TVS structure as that shown in FIG. 2 is also implemented in theTVS device 200. Between the isolation trenches 239 with the high sideand low side steering diodes isolated on two opposite sides of the P−epitaxial layer 210-2, the TVS structure same as the structure 100 shownin FIG. 2 with a plurality of trenches filled with N+ doped polysiliconlayer 120 surrounded by N+ dopant regions 110 are formed to link the N+buried layer 220 to the Vcc pad 150. A low impedance connection to theN+ buried layer is then formed.

FIG. 4A-1 shows an equivalent circuit of the TVS device 200 of FIG. 4A.To an external device, the TVS device 200 functions with thecharacteristics just like a single Zener diode 230-4 having lowcapacitance, but internally the TVS device comprises a main Zener diode230-3 working in conjunction with a high side steering diode 230-1 and alow side steering diode 230-2.

FIG. 4B is a close up view taken a top portion of the TVS device 200 ofFIG. 4A showing the equivalent capacitances of the circuit wherein theSCR is configured so that the P− epitaxial layer 210-2 of the SCR isalso depleted. TVS device as shown has the benefit of significantlyreduced capacitance because of the extra junctions formed between thesePN interfacial layers. In the prior art, the high side diode onlycomprised a single PN junction. The capacitance from this singlejunction could be undesirably high, and at risk to process variations.In this invention the SCR 230-1 has three PN junctions, with threecorresponding capacitances 135-1, 135-2 and 135-3 in series, resultingin a low equivalent capacitance. In addition, the TVS of this inventionrequires less area than the two-series steering diodes. The TVS deviceof this invention has the additional benefit in lowering the capacitanceof the second (low side) steering diode 230-2. Without N− top dopantlayer 215, the PN junction of the low side steering diode 230-2 would bebetween the N+ contact region 240 and the P− epitaxial 210-2 resultingin a relatively high capacitance. In this invention, that PN junction isshifted to between the N− top dopant layer 215 and the P− epitaxial210-2, resulting in a lower capacitance due to the lower dopingconcentration of N− top dopant layer 215. The TVS device as shown canalso be conveniently integrated and manufactured by applying standardmanufacturing processes. As shown in the manufacturing processes below,compared with the conventional TVS devices, there are no extra masksrequired.

The TVS device of this invention can also be formed using oppositeconductivity types compared to those shown in FIG. 4A. In FIG. 4C, a TVSdevice 200′ is shown where the conductivity types of each region arereversed. For example, the substrate 205′ is now N+ rather than P+ andthe buried layer 220′ is now P+ rather than N+. The polarities of thesteering diodes 230-1′ and 230-2′, and Zener diode 230-3′ are alsoreversed. The first steering diode 230-1′ is still a depleted SCR, andserves as the high side steering diode, and is formed vertically up fromP+ buried layer 220′ to N− epitaxial 210-2′, to P− top dopant layer 215′to N+ contact region 250′. The second steering diode 230-2′ acts as thelow side diode. The main Zener diode 230-3′ is in the same relativeposition but has a reversed polarity, being formed from the P+ buriedlayer 220′ to the N− epitaxial layer 210-1′ below. Also the bottomelectrode 272 now functions as the Vcc terminal while a top electrode(not specifically shown) is electrically connected to the P+ buriedlayer 220′ to function as the ground terminal.

FIGS. 5A to 5K are a series of cross sectional views for illustratingthe processing steps to manufacture the low capacitance TVS device withdepleted SCR as shown in FIG. 4 of this invention. FIG. 5A shows aheavily doped P+ substrate 205 with a lightly doped bottom P− epitaxiallayer 210-1 grown over it. In FIG. 5B, a masked implant (mask not shown)is performed to form the N+ implant buried region 220 and P+ triggerimplants 221. In FIG. 5C, the top P− epitaxial layer 210-2 is grown overthe bottom P− epitaxial layer 210-1 followed by the diffusion of the N+implant buried region 220. In FIG. 5D a blanket implant is performed toform N− compensation layer 215 at the top of the top P− epitaxial layer210-2.

FIGS. 5E-5H illustrate the process of forming the TVS structure of FIG.2, which is similar to the process shown in FIGS. 3A-3E. In FIG. 5E, ahard mask (not shown) is formed on top of P− epitaxial layer 210-2 tofunction as a hard mask for carrying out a trench etch process. Aplurality of trenches 107 are formed in the top portion of the P−epitaxial layer 210-2. In FIG. 5F, a sacrificial oxide layer is formed(not shown) followed by a phosphorus dopant implantation through thetrenches 107 to form dopant regions 110 below the bottom surface of thetrenches 107. In FIG. 5G, the sacrificial oxide layer (not shown) isremoved followed by carrying out an in-situ polysilicon deposition toform the polysilicon layer 120 to fill in the trenches following by theetching back of the polysilicon layer 120 to the top surface of the N−compensation layer 215. Then, a mask (not shown) is applied to implantdopant ions, e.g., phosphorus or arsenide, to form regions 130 near thetop surface of the N− compensation layer 215 followed by removing themask (not shown). In FIG. 5H, a diffusion process at a temperature of1150 degrees Celsius is performed for 30 minutes for the dopant regions110 and region 130 to diffuse and merge together around the trenchesfilled with the polysilicon layer 120 and merge with the N+ buried layer220.

In FIG. 5I, a trench mask (not shown) is applied to open the isolationtrenches 239 followed by filling the trenches with insulation material(which may include a polysilicon center). In FIG. 5J, implant masks (notshown) are applied to form the N+ contact regions 40 and P+ contactregions 250 near the top surface of the N− compensation dopant layer 215to function as the low side and high side diodes. The N− dopant layer215 may be formed either by implantation, or by epitaxial growth. If topdopant layer 215 is formed by blanket implantation or epitaxial growth,this TVS device requires no extra masks compared to a similar TVS devicenot employing a depleted SCR. The configuration (e.g., doping profile,region widths) of the SCR may be selected so that the SCR is depleted ata zero bias. The manufacturing processes proceed with the formation ofthe top insulation layer 245, the metal contact layer 150 and theinput/output pad 270. In FIG. 5K, a bottom electrode 272 may be formedunder the P+ substrate 205 as the GND pad to complete the manufacturingprocesses of the TVS device.

According to above descriptions, this invention discloses a method formanufacturing a transient voltage suppressing (TVS) device. The methodcomprises steps of a) growing a lower epitaxial layer having a firstconductivity type on a semiconductor substrate of the first conductivitytype and applying an implant mask to implant a buried dopant layer ofthe first conductivity type then growing a top epitaxial layer of thefirst conductivity type on top of the lower epitaxial layer followed byblanket implanting a top compensation layer of a second conductivitytype near a top surface of the top epitaxial layer and opening aplurality of contact trenches in the upper epitaxial layer thenimplanting a trench-bottom dopant region of a second conductivity typebelow each of the contact trenches in the top epitaxial layer; b)carrying out a deposition process to form a conductive trench-fillinglayer to fill in the contact trenches followed by the etching back theconductive trench-filling layer to the top compensation layer followedby applying a mask to implant dopant regions near the top surface of thetop compensation layer followed by carrying out a diffusion process todiffuse trench-bottom dopant region to surround the contact trenches andto merge with the buried dopant layer; and c) applying a trench mask toopen a plurality of isolation trenches followed by filling the isolationtrenches with an insulation material. In an preferred embodiment, themethod further includes a step of d) applying a contact region mask toimplant contact dopant regions near a top surface of the topcompensation layer to function as a high side diode and a low sidediode. In another preferred embodiment, the method further includes astep of e) forming a top insulation layer and applying a mask to opencontact openings through the top insulation layer followed by formingand patterning a top metal contact layer to function as input/output padto contact the high side and low side diodes and Vcc metal contact forcontacting the contact trenches for electrically connecting to theburied dopant layer.

Although the present invention has been described in terms of thepresently preferred embodiment, it is to be understood that suchdisclosure is not to be interpreted as limiting. Various alterations andmodifications will no doubt become apparent to those skilled in the artafter reading the above disclosure. Accordingly, it is intended that theappended claims be interpreted as covering all alterations andmodifications as fall within the true spirit and scope of the invention.

We claim:
 1. A transient voltage suppressing (TVS) device formed in anepitaxial layer of a first conductivity type supported on asemiconductor substrate, and the TVS device further comprising: aplurality of contact trenches opened and extended into the epitaxiallayer of the first conductivity type wherein the contact trenches arefilled with a doped polysilicon layer of a second conductivity type andwherein the contact trenches are further surrounded by a heavy dopantregion of the second conductivity type to form a P-N junction with theepitaxial layer of the first conductivity type; and a metal contactlayer disposed on a top surface of the epitaxial layer of the firstconductivity type electrically connected to a Vcc electrode wherein themetal contact layer further directly contacting the doped polysiliconlayer and the heavy dopant region of the second conductivity type. 2.The transient voltage suppressing (TVS) device of claim 1 wherein: theepitaxial layer is a P-type epitaxial layer and the contact trenches arefilled with an N-doped polysilicon layer surrounded by an N-type heavydopant region to form the P-N junction with the P-type epitaxial layer.3. The transient voltage suppressing (TVS) device of claim 1 wherein:the epitaxial layer is an N-type epitaxial layer and the contacttrenches are filled with a P-doped polysilicon layer surrounded by aP-type heavy dopant region to form the P-N junction with the N-typeepitaxial layer.
 4. The transient voltage suppressing (TVS) device ofclaim 1 wherein: the contact trenches are filled with a N-dopedpolysilicon layer surrounded by a N-type heavy dopant region to form theP-N junction with a P-type epitaxial layer; and the contact metal layeris electrically connected to a cathode electrode.
 5. The transientvoltage suppressing (TVS) device of claim 1 further comprising: a topdopant layer of the second conductivity type disposed near the top ofsaid epitaxial layer of the first conductivity type; a buried dopantregion of the second conductivity type disposed below the contacttrenches and encompassed in the epitaxial layer; wherein said burieddopant region interfacing with an underlying portion of said epitaxiallayer to constitute a Zener diode for said TVS device; and a firstcontact region of the first conductivity type disposed on the top ofsaid top dopant layer of the second conductivity type over said burieddopant region, wherein the first contact region of the firstconductivity type, the top dopant layer of the second conductivity type,the epitaxial layer of the first conductivity type, and the burieddopant region of the second conductivity type constitute a verticalsemiconductor controlled rectifier (SCR) to function as a first steeringdiode of the TVS device and wherein the first contact region of thefirst conductivity type is disposed at a distance away and insulatedfrom the contact trenches, and the buried dopant region of the secondconductivity type further extends laterally and merges with the heavydopant regions of the second conductivity type below the contacttrenches.
 6. The transient voltage suppressing (TVS) device of claim 5further comprising: a plurality of isolation trenches isolating asection of said epitaxial layer of the first conductivity type and thetop dopant layer of the second conductivity type for isolating said SCRfrom the contact trenches.
 7. The transient voltage suppressing (TVS)device of claim 5 further comprising: a second contact region of thesecond conductivity type disposed at the top of said top dopant layer ofthe first conductivity type and laterally in opposite side of thecontact trenches from the SCR and first steering diode wherein saidsecond contact region interfacing with the top dopant layer forfunctioning as a second steering diode for functioning with said firststeering diode as a pair of steering diodes of said TVS device.
 8. Thetransient voltage suppressing (TVS) device of claim 5 furthercomprising: a second steering diode formed laterally away from the SCRand first steering diode, wherein said first and second steering diodesform a pair of a high side steering diode and a low side steering diodeon two opposite sides of the contact trenches surrounded by the dopantregions of the second conductivity type.
 9. The transient voltagesuppressing (TVS) device of claim 8 wherein: the second steering diodefurther includes a part of the top dopant layer of the secondconductivity type for reducing the capacitance of said second steeringdiode.
 10. The TVS device of claim 8 wherein: the first and secondsteering diodes are connected to an input/output (I/O) pad through thefirst and second contact regions of the first conductivity type,respectively, disposed near the top surface of the top dopant layer ofthe second conductivity type.
 11. The TVS device of claim 8 furthercomprising: isolation trenches surrounding the first and second steeringdiodes for insulating the first and second steering diodes disposed ontwo opposite sides of the contact trenches.
 12. The transient voltagesuppressing (TVS) device of claim 8 wherein: the first steering diode,the said second steering diode and the contact trenches are separated byat least one isolation trench.
 13. The transient voltage suppressing(TVS) device of claim 5 further comprising: a voltage breakdown (VBD)trigger zone formed with a high dopant concentration of the secondconductivity type in a Zener diode overlapping zone disposed in theepitaxial layer below said buried dopant region to control a voltagebreakdown.
 14. The transient voltage suppressing (TVS) device of claim 1further comprising: an insulation layer covering a top surface of thesemiconductor substrate having contact openings filled with a metalcontact layer to contact the contact trenches.
 15. The transient voltagesuppressing (TVS) device of claim 1 wherein: said first conductivitytype is P-type; and said semiconductor substrate is electricallyconnected to a ground voltage (GND) terminal.